<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Demo</title>
<style>
html,body{
  height: 100%;
  margin: 0;
  padding: 0;
  font-family: Helvetica;
  background-color: #fff;
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
}
#root{
  position: relative;
}
.demo{
  width: 640px;
  margin: 100px auto 0 auto;
  padding: 15px 0;
  border: solid 1px #ccc;
  border-radius: 3px;
}
</style>
</head>
<body>
<div id="root"></div>
</body>
</html>